There's a New Way to Force Restart on the iPhone 8-Here's How to Do It
Ditching the Home button also means finding a new way to
force your iPhone to restart
no longer works. Here's how to manually reboot your new
How to force restart your iPhone 8 or iPhone 8 Plus
has a useful guide for manually rebooting the iPhone 8 with a video tutorial, but it's a little tricky. You'll need to quickly press and release the Volume Up button, then do the same with Volume Down and finally hold down the Side button (previously known as the sleep/wake button) to force a restart.
The entire thing should take a little over 10 seconds. If you're successful, the screen will turn black and then the Apple logo will appear onscreen as the iPhone 8 begins to restart.
What to do if the force restart doesn't work
If your iPhone 8 is frozen or bricked and a force restart doesn't help, you still have other options before schlepping to the nearest Apple Store for help.
The first is recovery-mode, which requires connecting your iPhone to a Mac. Plug it in with a USB or Lightning cable. Then do a force restart, but keep holding the Side button even after you see the Apple logo onscreen. Eventually, you'll see an icon telling you to connect to iTunes. At this point you can release the Side button, then launch iTunes where you can either update or restore your iPhone 8's software. Once you're done, hold down the Side button again until the Connect to iTunes icon goes away.
If that still doesn't fix the problem you may need to change the firmware on your iPhone 8 with a Device Firmware Update. To get into DFU mode, connect your phone to a computer and do a force restart. When the screen turns black, keep holding the Side button while also holding down the Volume Down button for 5 seconds. Then let go of the Side button but keep pressing Volume Down for 10 more seconds.
The screen will stay black and you can launch iTunes on your computer. If it worked you should see a message that says "iTunes has detected an iPhone in recovery mode. You must restore this iPhone before it can be used with iTunes." When you're done, do a force restart to return your iPhone to regular use.
Check out the video below for more help, and if you still can't get your iPhone to work you can always head to the Apple Store for some in-person support.